Preheat the oven to 160°C (320°F) not fan-forced.
Grease the side and base of a deep 23 cm or 24 cm diameter (inside top measurement) round cake pan. I used a spring form pan for easy removal of the cake. Line base and side of the pan with non-stick baking paper, extending the paper a few centimetres above the top rim of the pan.
Place 250 grams of chocolate, butter, coffee and water in a large saucepan over low heat, stirring occasionally. When chocolate and butter have melted, remove mixture from heat and allow to cool to room temperature.
Sift the flour, cocoa powder and bicarbonate of soda together into a very large bowl.Add the caster sugar to the bowl with the flour mixture, and stir the ingredients together until well combined. For this recipe, we prefer to use a whisk to stir ingredients together. In a medium bowl, place eggs, oil, vanilla and buttermilk.Whisk the wet ingredients together until well combined.Add the egg mixture to the flour mixture and stir until well combined. Add the chocolate mixture to the egg and flour mixture in a three batches, stirring until combined after each addition.Pour mixture into prepared pan. Bake for about 1 hour and 15 minutes (24cm pan) or 1 hour and 30 minutes (23cm pan). Insert a thin-bladed knife or wooden skewer into the center of the cake to test whether it is cooked through. If the knife/skewer comes out clean or with moist crumbs (not gooey batter) attached, the cake is ready. If not, return the cake to the oven and bake for a further 5-10 minutes before testing again.When cooked through, remove cake from oven, cover with a clean tea towel and allow to cool in the pan. When the cake has cooled to room temperature, remove it from the pan. The top surface of the cake will probably have a crunchy crust, which you may wish to trim off.
Prepare the whipped heavy cream or any other kind of cake icing you wish. For the one that I used, just whisk the heavy cream until stiff peaks form, then gradually add the icing sugar and vanilla extract, and whisk until well combined. Do not over whip!
If you only have one layer, then spread the icing evenly and try to smooth it out as much as possible, decorate with whatever you desire.If you have two layers, then place one layer on a serving platter, spread 1/3 of the icing on top and even out. Place the second layer on top and cover evenly with icing on top and all sides. Refrigerate until ready to serve. Serve chilled. If you wish to make the cake with it's original Chocolate Ganache, please see notes below for the ganache recipe.Enjoy!